1. Field of the Invention
The present invention relates to a satellite broadcast reception converter for receiving electric waves transmitted from a satellite, and particularly to a satellite broadcast reception converter suitable for receiving circularly polarized electric waves transmitted from a satellite.
2. Description of the Related Art
A satellite broadcast reception converter mounted in an outdoor antenna device is equipped with a waveguide having a hollow structure to which electric waves transmitted from a satellite are incident, a probe disposed at a predetermined position in the waveguide, a short cap for reflecting electric waves propagating in the waveguide to make the probe detect the electric waves, a circuit board having a processing circuit for performing appropriate processing (amplification, frequency conversion, etc.) on signals detected by the probe, etc. and the circuit board is usually covered by a shield case.
There has been hitherto known one of such satellite broadcast reception converters in which a waveguide and a shield case are integrally formed by aluminum die casting and a circuit board and a short cap are fixed in the shield case. In this case, a probe is formed on the circuit board by pattern formation, and if the short cap is fixed to the shield case by plural screws after the circuit board and the short cap are successively installed in the shield case, the circuit board could be pinched and fixed between the shield case and the short cap.
Further, in a satellite broadcast reception converter mounted on an outside antenna device for example when a right-handed circularly polarized or left-handed circularly polarized electric wave transmitted from a satellite is received, it is necessary to convert the circularly polarized wave incident into the waveguide to a linearly polarized wave in the phase converter and couple the linearly polarized wave to the probe for reception.
Still further, there has been also known a satellite broadcast reception converter in which a waveguide having a horn portion is formed of alloy of aluminum, zinc, etc. by die casting and then a phase converter called as a ridge is integrally formed on the inner wall surface of the waveguide and a circularly polarized wave incident from the horn portion into the waveguide is converted to a linearly polarized wave by the ridge. That is, the circularly polarized wave corresponds to a polarized wave having the rotating composite vector between two linearly-polarized waves that are equal in amplitude and have a phase difference of 90 degrees therebetween. Therefore, when the circularly-polarized wave passes through the ridge, the phase difference of 90 degrees is set to zero, and thus it is converted to the linearly polarized wave.
However, in the conventional satellite broadcast reception converter described above, the horn portion having desired aperture diameter and length is integrally formed at the tip of the waveguide, and the ridge having desired length and extending in the axial line direction is integrally formed on the inner wall surface of the waveguide. Therefore, not only the waveguide must be designed to be long in the axial line direction and thus miniaturization thereof is disturbed, but also the ridge serving as the phase converter is designed in an under-cut shape to make and thus a metal mold for die casting is complicated. As a result, the manufacturing cost is increased.
Therefore, there has been recently proposed a satellite broadcast reception converter in which a dielectric feeder achieved by integrally forming a radiation portion and a phase converter is used, the radiation portion is projected forwardly from the open end of a waveguide and the phase converter inserted and fixed in the waveguide is intersected to a probe at an angle of about 45 degrees. In this satellite broadcast reception converter, when a circularly polarized wave transmitted from a satellite is incident from the radiation portion of the dielectric feeder, the circularly polarized wave is converted to a linearly polarized wave in the phase converter while propagating in the dielectric feeder, and the linearly polarized wave goes into the deep portion of the waveguide and coupled to the probe.
Accordingly, according to the satellite broadcast reception converter using such a dielectric feeder, it is unnecessary to form a horn portion and a ridge (phase converter) integrally with a waveguide, so that the shape of the waveguide is simplified and the manufacturing cost can be reduced. In addition, the phase difference to the linearly polarized wave is large even when the overall length of the dielectric feeder is set to a relatively short value, the overall length of the waveguide itself can be shortened.
According to the conventional satellite broadcast reception converters thus constructed, the waveguide and the shield case are integrally formed by using aluminum die casting, and the circuit board and short cap are fixed in the shield case by using the plural screws. Therefore, the angularity between the probe pattern-formed on the circuit board and the axial line of the waveguide can be kept, and electric waves propagating in the waveguide can be surely detected. However, plural screws are required to fix the circuit board and the short cap, and also a subsequent step of coating adhesive agent to prevent loosening of the screws is needed. Therefore, the number of parts and the number of working steps are increased, which greatly causes rise-up of the manufacturing cost of the satellite broadcast reception converter.
In the satellite broadcast reception converter using the dielectric feeder, there is a merit that the manufacturing cost can be reduced and it can be miniaturized because a waveguide having a simple shape and a short length is available, however, it has some problem. That is, although the dielectric feeder is formed by injection-molding synthetic resin material, occurrence of surface sink and bubbles in synthetic resin is generally intensified when it is contracted as the volume (volumetric capacity) thereof increases. Therefore, high dimensional precision is not achievable with the dielectric feeder which is achieved by integrally forming a radiation portion and a phase converter like the prior art described above. Particularly when polyethylene (PE) which is low in price and has a low dielectric dissipation factor is used as the material of the dielectric feeder, there is a problem that the contraction after the injection molding is large and occurrence of bubbles is remarkable, so that the dimensional precision of each part of the dielectric feeder is extremely lowered, and the reception efficiency of electric waves transmitted from a satellite is lowered.
The present invention has been implemented in view of the foregoing situation of the prior arts, and has an object to provide a satellite broadcast reception converter in which a waveguide and a short cap can be simply fixed to a circuit board having a probe, and also which is suitable for reduction of the manufacturing cost and miniaturization and can enhance the dimensional precision of a dielectric feeder.
In order to attain the above object, according to a first aspect of the present invention, there is provided a satellite broadcast reception converter characterized by comprising a circuit board having a probe, at least one waveguide formed of sheet metal disposed vertically to the circuit board and at least one short cap designed to have a bottom through which the open end of the waveguide is closed, wherein snap pawls formed at the open end of the waveguide are inserted into fit holes formed in the circuit board and the short cap is fixedly fitted to the snap pawls to pinch the circuit board between the waveguide and the short cap.
According to the satellite broadcast reception converter thus constructed, the circuit board can be pinched and fixed by the waveguide and the short cap through a simple work of fixedly fitting the short cap to the snap pawls by utilizing the characteristic of springs (spring elasticity) of the waveguide formed of sheet metal. Therefore, the number of parts and the number of working steps can be greatly reduced, so that the manufacturing cost of the satellite broadcast reception converter can be reduced.
In the above construction, it is preferable that the short cap is soldered to an earth pattern formed on the circuit board. In this case, if the short cap is fixedly fitted to the snap pawls under the state that cream solder is coated on the earth pattern in advance, then the short cap could be easily soldered to the earth pattern by melting the cream solder in a reflow furnace.
Further, in the above construction, parallel portions extending in the axial line direction of the waveguide are formed at four confronting positions on the peripheral surface of the waveguide, and a snap pawl is extensively equipped to the top of each parallel portion, whereby each snap pawl of the waveguide can be inserted into the corresponding fitting hole of the circuit board with no rattle, and the relative positioning between the waveguide and the probe can be surely performed.
Still further, in the above construction, it is preferable that the circuit board and the short cap are covered by the shield case, the waveguide is inserted through a through hole formed in the shield case and projected to the outside and also the circuit board is fixed in the shield case. When the waveguide to which high dimensional precision is required is separated from the shield case as described above, the management of the dimensional precision of the waveguide can be enhanced.
Still further, in the above construction, it is preferable that the shield case is formed of sheet metal, and support portions are formed at the peripheral edge of the through hole formed in the shield case by bending the shield case. This construction enables the peripheral surface of the waveguide inserted in the through hole to be surely supported by the support portions.
In order to attain the above object, according to a second aspect of the present invention, there is provided a satellite broadcast reception converter characterized by comprising at least one waveguide that is closed at one end thereof and opened at the other end thereof, at least one probe projecting in the center axis direction of the waveguide and at least one dielectric feeder that is supported by the waveguide and formed of synthetic resin, wherein the dielectric feeder comprises a first split body having a radiation portion projecting from the open end of the waveguide and a second split body having a phase conversion portion fixed in the waveguide, and a projection equipped to the second split body is inserted in a through hole formed at the center portion of the first split body to unify the first split body and said second body into one body.
According to the satellite broadcast reception converter thus constructed, the dielectric feeder is constructed by the unified first and second split bodies which are separated from each other. Therefore, the volume (volumetric capacity) of each of the first and second split bodies as a single body is reduced, so that occurrence of surface sink and bubbles can be suppressed. In addition, the dielectric feeder is divided at the portion at which the through hole and the projection are jointed to each other, and the dividing face is located at a position far away from the center of the first split body at which the electric field intensity is largest, so that an electrical adverse effect caused by the division can be suppressed.
In the above construction, it is preferable that the second split body is equipped with an impedance converter which is narrowed in an arcuate shape from the open end of the waveguide to the phase converter, the projection is equipped to an end face of the impedance converter and the first and second split bodies are jointed to each other at the end face of the impedance converter. By providing the impedance converter as described above, the reflection components of electric waves propagating from the radiation portion through the impedance converter to the phase converter can be greatly reduced. In addition, the phase difference to the linearly polarized wave is large even when the length of the portion extending from the impedance converter to the phase converter is reduced, so that the overall length of the waveguide can be greatly reduced.
In this case, the projection may be strongly engaged with the through hole, however, it is preferable that an engaging projection is formed on the inner wall surface of the through hole, and an engaging recess portion is formed on the outer wall surface of the projection, the engaging projection and the engaging recess portion being snap-jointed to each other. By using such snap-joint, even when there is some dimensional dispersion between the projection and the through hole, the projection and the through hole can be simply and surely jointed to each other. At this time, it is preferable that representing the length from the rear end face of said radiation portion to said engaging projection by A and representing the length from the end face of the impedance converter to the engaging recess portion by B, A and B are set to satisfy the relation of A greater than B because the engaging projection and the engaging recess portion can be surely snap-jointed to each other with no rattle.
In the above construction, it is preferable that the radiation portion is designed in a conical shape which forwardly expands from the open end of the waveguide like a horn, and the end face of the impedance converter is jointed to the rear end face of the radiation portion. With this construction, the dividing face vertical to the travel direction of the electric waves propagating in the dielectric feeder is reduced, so that the reflection of the electric waves at the dividing face can be reduced.